It is desirable to improve the efficiency of light-emitting crystal structures, such as light-emitting diodes (LEDs), because this would increase their scope of use in commercial applications. Efficiency can be improved in two ways: increase the external efficiency or increase the internal efficiency.
An improvement in external efficiency is achieved by extracting more light out of the structure. As well known by those skilled in the art light-emitting crystal structures have a critical angle where light reflected beyond that angle gets reflected internally and does not exit the structure. E.g., only about 5 percent of the light generated in conventional planar LED passes out of the LED, the rest being internally reflected. Efforts to extract more light include texturing planar LEDs to reduce the amount of internally reflected light.